1. Field Of The Invention
The invention relates to a device for the excitation of a discharge in a laser gas having at least two metal electrodes.
2. Prior Art
For the excitation of gas lasers, especially in CO.sub.2 high-power lasers, direct-current discharge is used in general. A distinction is made between longitudinal and transverse excitation. In the case of longitudinal excitation, two electrodes are arranged at the ends of a discharge tube, between which a discharge is ignited [Hiroyuki Sigawara et al., Rev. Laser Eng. (Jap.) 9 (1) 21-30, (1981)]. A drawback is the often quite high operating voltage of typically 10 to 20 kV. In the case of transversely excited lasers only significantly lower voltages of about 1 to 2 kV are necessary. In the latter case, however, it is difficult to extend the discharge onto the flat electrodes arranged parallel to the discharge region. This can preferably be reached by segmented electrodes, for example plates or pins, which are connected with the operating voltage via separate series resistors [U.S. Pat. Nos. 3,772,610; 864,961; Haruhiko Nagai et al., IEEE J. Quant. Electron. Vol. QE-18(3), 416-421, (1982)].
Homogeneous transverse excitation of a laser gas volume can be obtained in a particularly simple manner by using resistive electrodes consisting for example, of thoriated tungsten (U.S. Pat. No. 4,260,958). All of these excitation systems, however, have the same disadvantage that ohmic losses reducing the efficiency of the laser occur in the resistors which are necessary to stabilize the gas discharge.
Laser excitation systems which operate with alternating voltage do not have this drawback, since in this case it is possible to use capacitive or inductive stabilization impedances [Bondarenko et al., Sov. J. Quant. Electron. 10 (4), 443-445, (1980); Gavrilyuk et al., Sov. J. Quant. Electron. 326-328 (1979)].
It is known that in the case of high-power lasers, especially CO.sub.2 lasers, the laser gas has to be circulated very rapidly and passed through external heat exchangers in order to eliminate power dissipation. Therefore, the excitation systems must be designed such that they impede the gas flow to the minimum possible extent. In this respect such transversely excited systems are particularly favorable in which gas flow, gas discharge and optical resonator are orthogonally arranged with respect to each other. These systems have the major drawback, however, that the excited volume does not correspond to the resonator volume. In order to utilize the total excitation volume, complicated zig-zag resonator arrangements have to be used, in which an emission in the transverse lowest order mode which is necessary for many technical applications of lasers is difficult to reach. Longitudinal systems, on the other hand, in which the excitation system and the resonator are arranged on one axis along which also the laser gas flows, permit an optimum beam quality to be reached in a relatively simple manner. But, such systems have the disadvantage of high operating voltage and higher gas circulation losses.